Plasma processing has been conventionally employed in the manufacture of a semiconductor device, an LCD (liquid crystal display), or the like to carry out a predetermined processing, e.g., film formation, etching processing, or the like on a substrate to be processed, such as a semiconductor wafer or an LCD substrate, by using a plasma.
In case of a plasma etching process employing a parallel plate type etching apparatus, for example, a substrate to be processed is mounted on a mounting table (susceptor) installed in a plasma processing chamber, and a plasma etching is executed by allowing a plasma generated within the plasma processing chamber to act on the substrate to be processed. Conventionally, a so-called focus ring is disposed to surround the substrate to be processed in conducting such a plasma etching process for the purpose of, e.g., enhancing an in-surface uniformity of the plasma etching process by ameliorating a discontinuity of the plasma at a peripheral portion of the substrate to thereby improve an etching quality thereat (see, e.g., Japanese Patent Laid-open Publication No. 2002-246370, pages 2 to 5, FIGS. 1 to 6).
Referring to FIG. 8, there is illustrated a configuration of main parts of the parallel plate type etching apparatus performing such a plasma etching process. In FIG. 8, a reference numeral 50 represents a mounting table (susceptor) disposed in a plasma processing chamber (not shown).
The susceptor 50 further serves as a lower electrode and is of a substantially disk shape made of a conductive material, e.g., having an anodic oxide film (alumite) formed at the surface thereof.
Provided on a wafer mounting surface of the susceptor 50 for mounting thereon a semiconductor wafer W is an electrostatic chuck 51 including an electrode 51a embedded in an insulating film 51b formed of an insulating material. Further, an annular focus ring 52 is disposed on the susceptor 50 to surround the semiconductor wafer W.
The susceptor 50 is formed of, e.g., aluminum as described above. Therefore, if there exists on the susceptor 50 a portion directly exposed to plasma formed above the semiconductor wafer W, that portion may be sputtered by the plasma, and as a result an undesirable sputtered film containing, e.g., aluminum, may be formed on the semiconductor wafer W.
For this reason, a diameter of the wafer mounting surface (where the electrostatic chuck 51 is formed) of the susceptor 50 is set to be slightly (for example, about 4 mm) smaller than that of the semiconductor wafer W, as illustrated in FIG. 8. Further, by setting the inner diameter of a lower part of the focus ring 52 to be smaller than the diameter of the semiconductor wafer W, the lower part of the focus ring 52 is extended to a space below a peripheral portion of the semiconductor wafer W such that none of the top surface of the susceptor 50 is directly exposed when viewed from the top.
The top surface of the focus ring 52 is set to be substantially level with the top surface of the semiconductor wafer W. Therefore, a total thickness of the focus ring 52 is far thicker than that (e.g., about 0.8 mm) of the semiconductor wafer W.
As described above, in the conventional plasma processing apparatus, the focus ring is installed around the periphery of the substrate to be processed, to improve in-surface uniformity of plasma etching. However, there is still a need to further enhance the in-surface uniformity of plasma etching, which has not been satisfied with the plasma processing apparatus using such a focus ring.